To be fair, throughout most of history, as long as China was under unified rule, it was almost consistently had the largest GDP in the world for any political entity, usually amounting to 25% share of the global GDP.

Compared to their historical performance, China hasn't even reached its peak.

I'd say political turmoil and conquests didn't harm the Chinese economy that much, but political stagnation during the crucial 19th century did. It was first disinterest of the ruling class in international trade (admittedly this started much earlier), which effectively handed over a lucrative business to European powers, who could in turn outgrow China.

The same political stagnation, as long as losing their position of advantage, has made China completely miss out on industrialization which was a great multiplier for GDP growth. This explains how a smaller neighbor like Japan (which embraced industrialization and Western-style colonization) could quickly surpass China and threaten it.

> anytime they tried to achieve anything, they were either conquered by an aggressive imperial power

It seems to me, the opium wars and the resulting partitioning was solely a fault of the Qing government. Sure, the Brits were big bullies but China was playing on a home field and could overpower invaders with sheer numbers.

Qing state was already breaking from inside by then. No wonder the didn't survive long after.